Pacemakers, by Anthony LaViola and David Triffletti
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Revision as of 14:35, 18 January 2013
To understand the necessity of a pacemaker, first an understanding of the heart must be developed. The heart is made up of cardiac cells called myocardium cells. These cells are the muscular tissue that pumps blood through the circulatory system. A small group of cells called the sinoatrial node initiates an electrical pulse at the top of the heart. As this electrical pulse flows through the heart from top to bottom the cells contract, building up pressure on the chamber and pumping the blood. First the left and right atriums contract; the artioventicular node, which sends a second delayed signal to the left and right ventricles, receives the signal. This cycle is repeated to send blood to all parts of the body. 
A pacemaker is a device that is implanted into the chest cavity of a person to control the rhythm of their heart. Every human is born with a natural, biological pacemaker that controls the contractions of the heart to pump the blood through the body and meet the oxygen needs of every cell. In certain cases this biological pacemaker breaks down and does not work properly anymore causing heart arrhythmia, strokes, and various other heart problems. One way to alleviate this problem is to surgically implant an artificial pacemaker to automatically control heart contractions. A pacemaker controls the heart by sending a low energy electrical pulse from the top to the bottom of the heart replacing the biological sinoatrial node in the heart.  
1791 – Galvani discovered that an eel could electrically stimulate frog legs 
1862 – Walshe suggests that heart could be electrically stimulated 
1927 – Hyman designs an apparatus that could be used to maintain heart function 
1929 – In Sydney, Australia a baby was resuscitated using an electrical stimulus 
1932 – Hyman concluded with rhythmic electrical pulses a heart could be returned to natural rhythm 
1951 – Callahan and Bigelow conducted experiments stimulating sinoatrial nodes in dogs to restore natural rhythmic heart beat during hypothermia 
1954 – Hopps performed experiments on animals to test snaking wires through veins 
1958 – first successful external implanted pacemaker, Furman found that placing electrodes internally that less energy could be used, Arne Larrson received the first internal pacemaker  
1958 – present – pacemakers have become smaller, smarter and more durable
Health Issue Resolved By Pacemakers
One reason doctors recommend a pacemaker is for bradycardia. This is the slowing of the heartbeat to well below average. Beta blockers, a medication for _cardiac arrhythmia control may also affect the heart rate and necessitate the use of a pace maker. One consequence of a low heart beat can be a Strokes-Adams attacks, which is where a victim repeatedly has fainting spells due to low amounts of oxygen getting to the brain from the low heart rate.  
Another reason for getting a pacemaker is due to a heart block. Heart block is where the artioventicular node or signal transduction to the ventricles fails to be transmitted resulting in unresponsive ventricles of the heart. The heart’s sinoatrial node may also become damaged and in that case be replaced with a pacemaker. Sometimes if the heart is physically damaged it can affect heart rate and require the implantation of a pacemaker. 
Certain heart surgeries can be grounds for implanting a pacemaker into a patient. 
Types of Pacemakers
There are three different types depending on what is required for the patient:
Demand pacemakers monitor the heart and only send an impulse when the heart slows below average.
Fixed-rate pacemakers send a pulse at a fixed rate to maintain a normal heart rate.
Rate-responsive pacemakers monitor factors such as body temperature, oxygen levels and carbon dioxide levels to adjust the rate of pulses sent. This is based off of the demand of the body depending on physical activity at that moment.
There are three different ways the pacemaker can be set up:
A single-chamber has one lead coming from the pacemaker either leading to the right atrium or right ventricle.
A dual-chamber has two leads coming out of the pacemaker that attach to the right atrium and right ventricle.
A triple-chamber has three leads, one attached to the right atrium, one attached to the right ventricle and one attached to the left ventricle.
Implanting of Pacemakers
1. Drugs to help the patient relax will be administered through an IV line.
2. Local anesthesia will be administered to the patient to numb the area.
3. The doctor will insert a needle into a vein near the collarbone where the wires will be inserted.
4. The wires are inserted and guided by an x-ray machine that will be in real time.
5. After the wires are in place, a small incision in the chest for the pacemaker is made.
6. The pacemaker, which holds the battery and the generator, will slip through the incision and be placed under the skin
7. The wires will be attached to the main body of the pacemaker and tested.
8. The patient is kept overnight in the hospital for observation.
9. Patients can resume normal activity in as little as two days after the surgery.
10. Any heavy lifting may need to be put off for up to a month after the surgery.
11. Periodically the doctor will check the status of the pacemaker over the phone.
This whole procedure is done while the patient is awake but on local anesthesia.
Side Effects and Dangers of Pacemakers
Pacemaker surgery is a very safe procedure but there is a small chance of side effects. Possible side effects of pacemaker surgery include bleeding, swelling, infection or bruising. Other more severe possible dangers of the surgery are damage of the blood vessels or nerves near the surgical site, a collapsed lung, or puncturing of the heart wall.
(1) Anonymous Explore How the Heart Works. http://www.nhlbi.nih.gov.silk.library. umass.edu/health/health-topics/topics/hhw/ (accessed 02/18, 2012).
(2) Anonymous Pacemaker. http://www.mayoclinic.com/health/pacemaker/ MY00276 (accessed 02/18, 2012).
(3) Anonymous Explore Pacemakers. http://www.nhlbi.nih.gov.silk.library.umass. edu/health/ health-topics/topics/pace/ (accessed 02/18, 2012).
(4) ALTMAN, L. K. Arne H. W. Larsson, 86; Had First Internal Pacemaker. The New York Times 2002.
(5) Furman, S. In Principles and techniques of cardiac pacing Haper & Row, Publishers, Inc.: New York, 1970;.
(6) Siddons, H. In Cardiac pacemakers; Charles C Thomas Publisher: Springfield, Illinois, 1967;.
(7) Thalen, H. J. T. In The Artificial cardiac pacemaker. Its history, development and clinical application. Van Gorcum; Charles C. Thomas: Assen; [Springfield, Ill., 1969; .